Mixing rubber



A. E. JUVE MIXING RUBBER July 14, 1959 3 Sheets-Sheet 1 Filed Sept. 8.1953 m lq 3Q July 14, 1959 JUVE 2,894,280

MIXING RUBBER Filed Sept. 8. 1953 3 Sheets-Sheet 2 IN V EN TOR.

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A. E. JUVE MIXING RUBBER July 14, 1959 3 Sheets-Sheet 3 Filed Sept. 8.1953 flEihUE mmvm. E'L/U'VE BY United States Patent 2,894,280 MIXINGRUBBER Arthur E. Juve, .Akron, Ohio, assignor to The B. F. GoodrichCompany, New York, N.Y., a corporation of New York Application September8, 1953, Serial No. 378,975

15 Claims. (Cl. 18-2) This invention relates to plasticizing and mixingplas ticizable material such as rubberlike material. The invention hasspecial utility for plasticizing and mixing and intimately blendingrubber-like materials with each other and with various compoundingingredients used in manufacturing rubber products. Moreover, accordingto this invention such rubber stocks may be discharged from the mixingapparatus to subsequent processing operations in a continuous flow. Theterm rubber as used herein refers to extremely viscous materialscharacterized (at least before mixing) by the properties of nerve andextensibility, and includes natural rubber, and synthetic rubber-likematerials such as the polymers of diolefins represented by the copolymerof butadiene and styrene (GR-S); polymers of chloroprene (Neoprene);copolymers of isobutylene and isoprene (Butyl); copolymers of butadieneand acrylonitrile (Buna N); etc. This application is acontinuation-in-part of my copending application Serial No. 159,043, nowabandoned; filed April 29, 1950.

The compounding and mixing of rubber on a scale suitable for commercialoperations is presently accomplished throughout the rubber industry bywhat is known as batch mixing. For more than a century the open mill hasbeen the standard equipment for this purpose while in more recent yearsBanbury mixers have become prominent for mixing rubber. The success ofopen mill mixing is to a large extent contingent on the skill andjudgment of an operator and is relatively slow. Banbury mixing requiresmassive machinery and excessive amounts of power, and for efficient andeconomical operation, large quantities must be mixed in each batch. Itis difiicult to regulate the temperature of the mixture in batch mixingand the subsequent processing operations which receive the stock mixturemust be regulated to accommodate the intermittent delivery to it of themixed batches. The advantages of mixing rubber and supplying it to thesesubsequent processing stations in a continuous flow are obvious butprior to this invention there has been no equipment capable of blendingor mixing the rubber to satisfactory commercial standards in acontinuous flow.

Mixing equipment utilizing screws and the like have been proposed whichoperate successfully for continuously mixing many organic plastics suchas the vinyl polymers, cellulose polymers and the like, but thisequipment is inadequate for mixing rubber and rubber-like materials.Ordinarily rubber materials require some preliminary breaking down ormastication to reduce their viscosity before they can be blendedsuccessfully in a mixture, especially where ingredients mixed includefinely-divided pigments, whereas the organic plastics noted in thepreceding sentence do not require such mastication. Usually theseplastic materials tend to soften readily under the influence of heat inmixing equipment and appear to, wet pigments and the like rather easilyso See that a mixing action which consists essentially of merely foldingthese plastics and ingredients into each other is satisfactory but thismixing action is not suitable, for rubber. There is also adequateequipment available for simply masticating or plasticizing rubber butthe action of this masticating equipment is not suitable for performingthe added function of adequate mixing.

According to this invention rubber and other plasticizable materials canbe mixed, blended and plasticized in a single piece of equipment toacceptable commercial standards and discharged to subsequent processingequipment in a continuous flow. The preferred apparatus of thisinvention is characterized by a rotor having longitudinal ribs whichrotates inside a passage extending through a stator. The improved mixingaction as well as the mastication essential to efiicient mixing ofrubber and pigments is obtained in accordance with the princiciples ofthis invention by the cooperation of the face of the ribs which ispresented to the rubber and the surface of the passage through thestator which surrounds the rotor and against which the rubber is mulledand worked by the ribs. As the rotor rotates inside the stator the faceof each rib leading the rib in the direction of rotation is shaped toforcibly smear the ingredients of the mixture together against the wallsof the stator and simultaneously stretch the mixture bothcircumferentially and lengthwise of the rotor. The power requirements donot exceed that required for mixing comparable quantities of rubber onopen mills and are considerably less than that required for Banburymixing. Further the temperature of the mixture can be accuratelyregulated with this equipment as well as the rate at which the mixing isaccomplished so that the mixing may correspond to the operation of anyparticular subsequent processing equipment to which the mixture is to bedelivered.

The invention will be more fully explained in connection with theaccompanying drawings which illustrate preferred mixing apparatusconstructed in accordance with and embodying the invention.

In the drawings:

Fig. 1 is a side elevation partially in section showing one preferredform of mixing equipment embodying this invention;

Fig. 2 is a cross-sectional view taken on the line 2-2 of Fig. 1;

Fig. 3 is a view showing the cross-sectional shape of the ribs on themixing surface of the rotor, and illustrating the typical mixing actionof the equipment Fig. 4 is another view showing the cross-sectionalshape of the ribs on the mixing surface of the rotor and illustratingvarious details about the shape of the ribs;

Fig. 5 is a side elevation of another form of mixing equipment embodyingthe invention;

Fig. 6 is a cross-sectional View taken on the line 66 of Fig. 5;

Fig. 7 shows a side elevation of another preferred type of rotor whichmay be used in the equipment shown in Fig. 5;

Fig. 8 is a fragmentary view showing another form of rotor and portionsof the corresponding stator in which it is positioned which may be usedin practicing the invention;

Fig. 9 is a cross-sectional view taken on the line 9-9 of Fig. 8;

Fig. 10 is another view similar to Fig. 8 but showing another type ofrotor and stator which maybe used in practicing the invention;

Fig. 11 is a cross-sectional view taken on the line 11-11ofFig. 10; 1 ii l Fig. 12 is a fragmentary" view showing the side elevation of a rotorand stator generally similar to that shown in Fig. but having differentmechanism for feeding rubber to the rotor and the stator.

The mixing equipment shown in Figs. 1 and 2 includes a stator 19 havingan interior passage 11 formed by a smooth concavely-curved surface ofrevolution 12v of circular cross-sectional shape which extends throughthe stator from one end to. the other. A rotor 13 extends coaxiallythrough this passage in the stator and the rotor has a mixing surface 14along the portion of the rotor surrounded by the surface 12. Theinterior surface 12 of the passage 11 and the mixing surface 14 of therotor cooperate between them to define a mixing chamber 15 (see Fig. 2)which receives rubber and other ingredi cuts of the mixture and in whichthe mixing is effected. The. ends 16 of the rotor project beyond theends of the stator and they are journalled in bearings 17 mounted on aframe 18 which also supports the stator. One end 16a of the rotor (theright end as it is viewed in Fig. 1) extends through its respectivebearing 17 and is keyed to a coupling 19 engaged with a drive unit 20which pro- Yides a source of power for rotating the rotor inside thepassage 11.

The stator is secured to the frame 18 by several bolts 22 which extendthrough slots 23 disposed longitudinally of the stator in the flanges 24along the lower edges of the stator. The stator is constructed of anupper housing 27 and a lower housing 28, which are fastened together inmating relation as shown in Fig. 2 by cap screws 29. The upper and thelower housing each have a semi-circular wall 30 extending the length ofthe housing and when the housings are assembled together, the concavesurfaces of these walls 30 cooperate to form the surface 12 whichdefines the passage 11 through which the rotor 13 extends. The upperhousing may be removed from the assembly for cleaning, repairs, andinspections of the rotor by removing the cap screws 29. Both the upperand lower housing contain passages 31 connected by a conduit 32 throughwhich steam or other thermal medium may be circulated to regulate thetemperature at which the mixing is car ried out.

The rubber and other materials to be mixed together during operation ofthe equipment are charged into the mixing chamber in a continuous flowthrough the openings 33 and 34 which extend from the top surface of thestator downwardly into the mixing chamber. The rubber may be in the formof pellets, strips, small chunks or the like and suitable equipment (notshown) may be provided for feeding other ingredients at the ratesdesired. In the mixing chamber the action of the rotor (as will be morefully explained subsequently) is smeared against the surface 12 of thepassage 11 and is worked progressively toward the discharge end 35 orleft end of the stator as it is shown in Fig. l. The mixing surface 14of the rotor extends slightly beyond the discharge end 35 of the statorto facilitate the removal of the mixed rubber from the stator and asuitable receptacle 36 is provided under the discharge end of the statorto receive the mixture. Instead of the receptacle 3,6,, the mixture maybe discharged to a suitable conveyor or other means for transferring itto subsequent processing operations.

The charging openings 33 and 34 are spaced apart longitudinally on thestator because it is generally desirable to add various compoundingingredients to rubber at different stages of the mixture. For example,in a typical rubber compound the rubber stock, plasticizers andsofteners, etc., may be charged into the opening 33' near the front ofthe stator. These ingredients are then masticated and mixed and advancedby the rotor toward the discharge end 35 and when this, portion of themixture reaches the rearward opening 34,, then such ingredients ascarbon black, accelerators, and sulfur may be added to the mixture.Since the opening 33 is normally the one through which the rubber willbe charged into the mixing equipment, it is somewhat wider than theopening 34. However, each of the openings are of substantially identicalshape and are designed to funnel the materials into the mixing chamber15. In each of the charging openings the opposite sides 37 (Fig. 1) areperpendicular to the axis of the rotor. The third side 38 (see Fig. 2)of each charging opening is a plane surface which is parallel to theaxis of the rotor and disposed substantially tangentially to the surface12 of the mixing chamber. The fourth side 39, opposite side 38, isinclined inwardly from the top of the stator toward the tangential side38. The material fed into these openings normally drops into the spaceat the bottom of the opening close to the tangential side 38 and therotor is rotated against this material in a direction such that theportion of the rotor exposed at the bottom of the charging opening movestoward the tangential side 38 or, in other words, counter-clockwise asviewed in Fig. 2. Thus, the mixing surface of the rotor progressivelyforces, portions of this material into the mixing chamber 15.

The mixing surface 14 of the rotor is formed with av plurality ofprotruding ribs 40 which extend longitudinally along the rotorapproximately along a generatrix of the surface of revolution 12 andwhich are spaced apart by flutes 41. The ribs 40 have a gradual helicalspiral throughout the length of the rotor which is in the same directionas the rotational direction of the rotor. The mixing surface of therotor is also gradually tapered from a narrow portion at the front ofthe stator to a wider portion at the discharge end 35 of the stator andthe surface 12 of the passage 11 is also tapered to the same extent. Thetaper of surface 12 and of the rotor, and, also the helical spiral ofthe ribs 40 contribute to the mixing action as will be subsequentlyexplained. Addi-v tionally, the taper of these portions is convenient toper mit adjusting the rotational clearance between the ribs of themixing surface of the rotor and the surface 12 of passage 11 by changingthe relative. longitudinal position between the rotor and the. stator.In this embodiment of the invention, this may be accomplished byloosening the bolts 22 which fit through longitudinal slots 23 in theflanges 24 of the stator and then moving the stator toward or away fromone end of the rotor to provide the. clearance desired. There is aseries of such mixing zones defined by the leading faces of the ribs andthe opposing mixing surface 12 of the stator, the mixing zones beingcircumferentially spaced apart and each being generally wedge-shaped incross section.

The cross-sectional shape of the ribs 40 and the flutes, 41 is moreclearly brought out in Figs. 3 and 4 in which they have been drawn to anenlarged, scale. Each. of the ribs has a crest 44 spaced from thesurface 12 of the passage 11 at the desired rotational clearancedetermined by the relative longitudinal position of the stator and therotor. The leading face 45 of each rib which is presented to the rubbermaterial during mixing is shaped so that it recedes from the crest 44toward the flutes 41 in a gradual curve, convex toward the, surface 12of the passage 11 so as to define with the surface 12 a mixing zoneconverging toward crest 44. The size and shape of each rib issubstantially the same. throughout the length of the rib and thedifference in area of the working surface 14 of the rotor from the frontto the discharge end due to the taper is accommodated by making theflutes wider near the discharge end. The curved shape of the leadingface 45 of each rib becomes gradually steeper toward the base of the,rib and then blends smoothly into the concave or reverse curvature oftheiflutes 41. Between the crest; 44-. and the bottom of each flute 41the shape ofthe leadingface '45 of each rib is in cross-sectional shape,a re verse or ogee curve. inthe preferred apparatus.

The. face 46 of each rib on the side which trails or follows the crest44 with respect to the rotational direction of the rotor hassubstantially the same cross-sectional shape as the leading face 45. Inthe form of the invention illustrated, the preferred shape of the ribsis that from one flute to the next adjacent flute the surface of theribs is in cross-section a circular arc which connects the curvature ofthe flutes tangentially. It can be seen in Fig. 3 that the shape of theleading face 45 of each rib is such that there will be a space ofappreciable width between the surface 12 of the passage 11 and thebottom of each flute and that this space is. progressively narrowertoward the crest 44 of each rib.

In operating the equipment the rubber and the ingredients to be mixedare charged into the mixing chamber 15 at a rate such that the mixingchamber is not completely filled by the rubber. The rotation of therotor against rubber charged into the opening 33, for example, dividesthe rubber into relatively small banks 48 between the convexly curvedleading faces 45 of each rib of the rotor and the surface 12 of thepassage 11. The rotation of the rotor exerts pressure on each of thesebanks tending to urge them radially outward and this pressure is opposedby the surface 12 of the passage 11. The resultant of these opposingforces ap parently tends to tumble the banks in a direction parallel tothe ribs 40 and to force the bank toward the crest of each rib bysliding it up the convex leading face 45 of the rib. Thus the bank iscontinuously being forced into the narrow space between the surface 12of the passage 11 and the crest 44 of the rib where it is forciblysmeared by the rib against the surface 12 of the passage.

1With the continued rotation of the rotor, a portion ofeach bank isprogressively removed from each bank and is forced between the crest 44and the mixing surface 12 in the form of a thin sheet. This portion isalso apparently stretched in a direction longitudinally of the rotortoward the discharge end 35 of the stator. This is believed to be causedby both the helical spiral of the ribs and also the fact that the taperof the rotor and surface 12 increases the volume of the mixing chambertoward the discharge end. Each rib is continuously trying to compressits respective bank 4% into the narrow opening between thecrest 44 andthe surface 12 and since rubber is essentially incompressible, theportion sheeted out of the bank at the top of the crest will naturallyflow toward the portion of the mixing chamber of greater volume. Thereis also believed to be some stretching of the rubber in a directioncircumferentially of the rotor but the major stretching occurs inthelongitudinal direction. It will be noted in the drawings that thedischarge opening from the mixing chamber is a non-throttling opening;i.e. the opening is unobstructed so that the stock banks or ribbonsemerge freely from the discharge opening without any appreciable backpressure being built up inside the mixing chamber.

Substantially as fast as the portion of each bank is urged across thecrest 44 it is assimilated into the bank of material on the nextsucceeding rib and thus there is a continuous interchange of smallquantities of material from bank to bank and each of these quantities isforcibly smeared against the surface 12 by the rib as it is beingtransferred to another bank. The stock emerges from the discharge end ofthe rotor in long twisted ribbons. The action of the rotor has beenfound to be self-- cleaning. In the event that a particularly sticky ortacky stock adheres to the mixing surfaces inside, the equipment may becleaned by merely dropping into the hopper 33 a rubber which isrelatively dry and which will mix with the tacky stock, and in turn bedischarged from the end of the rotor.

The smearing and stretching action of the ribs is generally comparableto the smearing action obtained in open mill mixing and this apparentlytends to break down the nerve of the rubber and at the same time crushthe finely-divided ingredients into the particles of rubber. Toinvestigate the actual distribution of the ingredients mixed in thisequipment a rubber which was colored white was added at the firstopening 33 in. the equipment shown in Fig. 1 and then a very smallquantity of carbon black added at the second opening. After a briefperiod of mixing before the stock reached the discharge end of thestator, the upper housing 25 of the stator was removed, and it was foundthat the stock was uniformly gray throughout.

The dispersion of carbon black into rubber has also been studied by thefollowing test: Fifty parts of Easy Processing Channel Black and 100parts of Butyl rubber (copolymer of isobutylene with a small proportionof butadiene or isoprene) were mixed by passing the ma terial oncethrough apparatus similar to that of Fig. 1 while it was maintained at atemperature of about F. and the clearance between the ribs of the rotorand the surface 12 of the stator at about .003 to .004 inch. The mixedrubber stock collected at the discharge end was then dissolved in carbontetrachloride and deposited on electron microscope slides. The rubber onthe slides was then evaporated leaving the channel black on the slides.The same composition of rubber was also prepared on an open mill at thesame temperature and with substantially thesame clearance. Examinationof the slides of each of these compositions under the electronmicroscope showed distribution of the channel black was as uniform inthe equipment of this invention as with that mixed in the open mill.

The particular shape of the leading face 45 of each rib is determinedwith regard to the coeflicient of sliding friction between the mixtureand the face 45 of the rib. It is desirable that the rubber tend toslide up the leading face 45 toward the crest of the rib under therotational pressure to obtain the desired smearing action. While thereis believed to be a critical angle at which the leading face 45 of eachrib should be inclined for each material, it is obviously impractical toattempt to design equipment for exactly each material mixed and also inthe course of making a single mixture the coefiicient of friction willchange during the various stages of the mixture. The curvature of theleading face 45 as shown in Figs. 3 and 4 is such that for mixing amaterial having a low coefficient of friction on the surface of theribs, substantially all the bank will be urged toward the crest duringthe rotation, whereas if the coefficient of friction is high, at leastthe portions of the bank nearer the crest will be urged toward thecrest.

Fig. 4 shows further details about the shape of the leading face 45 ofeach rib on a rotor which has been found suitable for mixing rubbercompounds. As indicated in Fig. 4, a line T tangent to the leading face45 at the point 49 where it blends into the curvature of the flutesmakes an angle a of about 40 with the line R connecting the crest 44 andthe rotational axis of the rotor. Preferably for mixing rubber thisangle will always be greater than about 25. Tangents T T etc. to theleading face 45 at other points between the point 49 and the crest 44make a progressively greater angle with the line drawn from the crest tothe axis of the rotor.

Additionally this rotor and the surface of the passage in which therotor operated were tapered from the front toward. the discharge end 35of the stator and an angle of 0--46' with respect to the rotational axisof the rotor. The lead of the helical spiral of the ribs was such thatthe ends of the ribs at the discharge end of the rotor were offset anangle of 71 -15' from the ends of the same ribs at the forward end ofthe rotor and the mixing surface 14 of the rotor was approximately one(1) foot long. The mixing surface 14 contained nine ribs, equallyspaced, and the cross-sectional shape of the ribs from one flute to thenext was a circular arc having a radius of 0.375 inch.

; An example'of a typical'mixture or rubber stock compounded in thisequipment is as follows:

. Example 1 A stock was mixed according to the following recipe:

rubber and curing agents (zinc oxide, sulfur and accelerator) were addedat the first hopper and the carbon black by means of an automaticdispenser at the second hopper. The rubber and curing agent were addedin small portions at frequent intervals to simulate continuous feeding.The temperature of the stator jacket was controlled at the level between70 and 80 F. and the rotational clearance between the crest 44 of theribs and the surface 12 of the passage 11 was .012 inch. The stockmixture issuing from the discharge end 35 of the stator was shiny andwould not mark white paper. It was of acceptable commercial standard.

Example 2 Another stock was prepared according to the following recipe:

Material: Parts by weight Hycar 1001 100.0 Zinc oxide 5.0 Accelerator1.0 Easy Processing Channel Black 50.0 Sulfur -1 1.5

The accelerator was benzothiazyl disulfide. This stock was mixed in thesame equipment and under the same conditions as the stock in Example 1.The stock mixture issuing from the discharge end was shiny and black andwould not mark white paper.

Figs. -12 show various types of mixing equipment embodying theprinciples of this invention.

In the embodiment of the invention shown in Figs. 5 and 6, the stator 50is constructed in substantially the same manner as the stator of Fig. 1,and it is adjustably secured to a frame 51 by an adjusting screwmechanism 52. Through the stator 50 there is a longitudinal passage 53in which a rotor 55 is rotatably supported by a bearing 56 at the leftend of the rotor. The rotor 55 along the portion enclosed by the passage53 has a mixing surface 57 which includes longitudinal ribs 58 spacedapart by flutes 59, each having the same cross-sectional shape as theribs 40 and flutes 41 described in Figs. 1-4 except that in Fig. 5 theribs 58 are not disposed helically along the rotor but extend generallyparallel to the rotational axis of the rotor. The mixing surface 57 ofthe rotor is gradually tapered from the front end 60 to the dischargeend 61 adjacent bearing 56. The surface of the passage 53 is alsotapered the same extent. The rotor is also hollow as indicated at 62 inFig. 6 so that a thermal medium may be circulated through the rotor aswell as the stator.

The substantial difference between the embodiment shown in Fig. 5 andthat in Fig. 1 is in the mode in which the stock is delivered to themixing chamber. In the species shown in Fig. 5, the forward end of thestator surrounding end 60 of the rotor has a tube 64 secured toit whichextends coaxially of the rotor forwardly from the front end of thestator. The tube 64 has an opening 65 in its upper side near the endremote from the stator through. which rubber and ingredients may becharged into the tube. In the tubethere is a plunger 66 which isoperated by a pressure cylinder 67 to urge the plunger toward and awayfrom the stator inside the tube. The stroke of the plunger 66 isregulated so that with the plunger withdrawn to the right the opening65- is exposed for insertion of the material and as the plunger is movedtoward the stator, the material is delivered to the front end 61 of therotor.

The front end 60 of the rotor has a smooth surface and is shapedessentially like a paraboloid. This smooth surface blends smoothly intothe ribs 58 and flutes 59 so that material urged against the end 60 ofthe rotor is channeled over this end surface and inside the passage 53through the stator. The speed at which the plunger operates is regulatedso that the material does not com: pletely fill the flutes 59 and otherspaces between the ribs. As the rotor is rotated, the mixing action isessentially the same as described in connection'with the rotor 13 inFig. 1. The rubber mixture due to the tapered shape of the rotor and ofthe rotation of the rotor is worked rearwardly toward the discharge end61 of the rotor and issues from the stator into a suitable receptacle 63supported on the frame 51. The rubber mixture advances through thestator toward the discharge end 61 by the mixing action imparted to itby the rotor, the plunger functioning to deliver the material to thestator.

The rotor 70 shown in Fig. 7 differs from the rotor of Fig. 5 in thatthe rotor in Fig. 7 has gradually helically disposed ribs 71 rather thanstraight ribs. The rotor shown in Fig. 7 may be substituted for thatshown in Fig. 5 with equal efiiciency.

The modification of the invention illustrated in Fig. 8 differs fromthat shown in Fig. 5 in that the rotor 75 is not tapered and the passage76 through the stator 77 in which the rotor operates is cylindrical.

The modification of the invention illustrated in Figs. 10 and 11 differsfrom that shown in Fig. 5 in that the rotor 80 employed has essentiallya smooth tapered mixing surface 81 and the surface of the passage 82through the stator 83 in which the rotor is mounted has alternatelyspaced ribs 84 and flutes 85 extending the length of the stator. Themixing action obtained with this rotor and stator are essentially thesame as that described in connection with the rotor 13 of Fig. 1.

The modification of the invention shown in Fig. 12 differs from thatshown in Fig. 5 in that a screw is substituted for the plunger 66 tofeed the material to the end of the rotor 91 in the stator 92. The screwadvantageously provides for continuous feeding of the rubber into themixing chamber and is somewhat more conveniently used in many operationsin place of the plunger 66 of Fig. 5.

Variations of the invention may be made within the scope of theaccompanying claims.

I claim: 7

1. Apparatus for mechanically homogenizing and kneading plastic massescomprising a rotatable conical body and a closely adjacent surroundingconical sleeve forming a conical space which is of substantially uniformwidth throughout its length and is entirely open and unobstructed at itsgreatest diameter, means for introducing a plastic mass into the spacebetween said body and said sleeve in the vicinity of the smallerdiameter of said body, and space ribs on said rotatable conical bodyapproximately filling the space between said body and said sleeve andextending in the general direction ofthe axis of said body.

2. Apparatus according to claim 1, in which said ribs are arrangedslantwise with respect to the axis of said rotatable body. 7

3. Apparatus for mechanically homogenizing and kneading plastic massescomprising a rotatable generally conical body and an adjacentsurrounding enerally conical sleeve forming an annular mixing chamberwhich is of substantially uniform width throughout its length and whichhas a non-throttling discharge opening at. its greatest diameter, meansfor introducing aplastic mass has into the space between the body andsaid sleeve in the vicinity of the smaller diameter of said body, andspaced ribs on said rotatable body approximately filling the spacebetween said body and said sleeve and extending in the general directionof the axis of said body, each said rib having a smooth crest and aleading face blending into said crest in a smooth convex curve, saidleading face slanting gradually away from the opposing surface of saidsleeve and defining therewith and with said crest a generallywedge-shaped mixing zone, communicating with said non-throttlingdischarge opening.

4. Apparatus according to claim 3 wherein said ribs are disposed at anangle to the axis of said rotatable body.

5. In an apparatus for mechanically plasticizing and mixingplasticizable material, the combination consisting of two concentricrelatively rotatable mixing members one of which has an annular mixingsurface which is circumferentially continuous and the other of whichpresents a plurality of circumferentially spaced-apart local mixingsurface regions in opposed relation to said annular continuious mixingsurface, said members defining between their respective mixing surfacesand annular mixing chamber; means for introducing a charge ofplasticizable material into said mixing chamber at a predeterminedcharging zone of said chamber; a non-throttling discharge opening fromsaid mixing chamber in a location thereof spaced from said chargingzone; said local mixing surface regions being oriented so that eachslants gradually away from said opposing continuous mixing surface inthe circumferential direction thereof and each said local region atleast along its portion closest to said continuous surface being curvedconvexly to said opposing continuous surface, said gradually slantinglocal mixing surface regions forming with said continuous mixing surfacea series of circumferentially spaced mixing zones of generallywedge-shaped cross section which series of wedgeshaped zones extendscontinuously between and communicates with said charging zone and saiddischarge zone; and means for relatively rotating said members to dividea charge at said charging zone into individual wedgeshaped banks in saidmixing zones and to advance said banks through said mixing zones byprogressively squeezing the banks toward the narrower regions of themixing zones and to discharge said banks without throttling the flowthereof.

6. In an apparatus for mechanically plasticizing and mixingplasticizable material, the combination consisting of two concentricrelatively rotatable mixing members having opposing mixing surfacesdefining an annular mixing chamber; means for introducing a charge intosaid mixing chamber at a predetermined charging zone therein; anon-throttling discharge opening from said mixing chamber at a locationremote from said charging zone; one of said mixing members having itsmixing surface annular and circumferentially continuous between saidcharging zone and said discharge opening, the other of said mixingmembers having on its mixing surface a plurality ofcircumferentially-shaped ribs extending generally lengthwise of themixing chamber from said charging zone to said discharge opening, theribs having crests closely spaced from the opposing annular mixingsurface and leading faces which slant gradually toward the opposingannular mixing surface in the circumferential direction of the latter assuch faces approach their respective crests thereby defining a series ofcircumferentially spaced gradually converging mixing zones generally ofwedge-spaced cross section, said series of wedge-shaped mixing zonescommunicating both with said chraging zone and said discharge openingand extending continuously therebetween, and means forrelativelyrotating said mixing members to sub-divide a charge at iiisaid charging zone into wedge-shaped banks in said mixing zones and toadvance said banks lengthwise through said zones by progressivelysqueezing the banks toward the narrower regions of said mixing zones andto dis charge said banks without throttling at said discharge zone.

7. Apparatus according to claim 6 wherein the leading face of each ribblends smoothly into its respective crest in a curve convex to theopposing annular mixing surface.

8. Apparatus according to claim 6 wherein the leading face of each ribis curved convexly to said opposing annular mixing surface so that saidmixing zones in cross section are shaped generally like one of thevertex regions of a crescent.

9. Apparatus according to claim 6 wherein one of said mixing members isa tubular stator and the other is a rotor extending through the stator.

10. Apparatus according to claim 6 in which said ribs are disposedhelically relative to the rotational axis of the mixing members.

11. The apparatus of claim 6 in which said annular mixing surface of onemixing member and the other mixing member along the regions of thecrests of said ribs are generally tapered away from the rotational axisof the mixing members in the direction of the discharge opening so thatsaid annular mixing chamber progressively increases in volume from theregion thereof adjacent said charging zone.

12. Apparatus according to claim 6 wherein said means for introducing acharge into said mixing chamber includes means disposed axially of themixing chamber for forcing the charge toward said chamber.

13. Apparatus according to claim 6 wherein said means for introducing acharge into said mixing chamber is a feed screw disposed axially of themixing chamber.

14. Apparatus according to claim 6 wherein said means for introducing acharge into said mixing chamber is an opening through one of said mixingmembers into the mixing chamber transverse to the rotational axis ofsaid members.

15. The method of mechanically plasticizing and mixing plasticizablematerial which comprises introducing a charge of material into apredetermined charging zone of a confined annular mixing chamber definedby opposing annular concentric mixing surfaces; limiting the quantity ofcharge introduced to a volume smaller than the volume of the mixingchamber; relatively rotating said mixing surfaces to subdividesubstantially the entire charge into a plurality of individualcircumferentiallyspaced wedge-shaped banks confined between localopposed regions of the mixing surfaces defining a series ofcircumferentially-spaced wedge-shaped mixing zones, and to advance saidwedge-shaped banks lengthwise of the mixing chamber in such mixing zonestoward a discharge opening remote from said charging location;maintaining the progression of said banks toward said discharged openingprimarily by the squeezing pressure on the banks as they are urged intothe narrower regions of said mixing zones as a result of said relativerotation of said mixing surfaces; maintaining said banks free fromthrottling as they are so advanced in said zones; and discharging saidbanks without throttling through said discharge opening.

References Cited in the file of this patent UNITED STATES PATENTS1,508,109 Lovejoy Sept. 9, 1924 2,295,362 Schnuck Sept. 8, 19422,453,088 Dulmage Nov. 2, 1948 2,779,054 Doriat et a1. Ian. 29, 1957UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,894,280

' July 14, 1959 Arthur Ea Juve It is hereby certified that error appearsin the printed specification of the above numbered patent requiringcorrection and that the said Letters Patent should readas correctedbelow,

Column 8, line 62, for space read m spaced column 9, line 58, for"shaped" read spaced line 62', for "spaced read shaped line 69, for"chraging" read charging Signed and sealed this 29th day Of December1959 (SEAL) Attest:

KARL Hn AXLINE ROBERT C. WATSON Attesting Officer Commissioner ofPatents

